A total of 17 endophytic fungal isolates were obtained from the leaves of Mentha cordifoliaOpiz (Lamiaceae). Seven isolates were identified to the level of genus by using taxonomically relevant morphological traits. Colletotrichumand Phomopsisspecies were dominant among these strains. All strains were separated from M. cordifolialeaf for the first time. The ethyl acetate extracts of all endophytic fungi were tested for antibacterial activity against Salmonella typhimuriumTISTR1166 and Pseudomonas aeruginosaTISTR781. Most endophytes exhibited antibacterial activity. Ustilagosp. MFLUCC15-1024 presented the highest inhibition zone diameter with a MIC of 31.25 μg/mL against the tested pathogens. The chemical composition of the ethyl acetate extract of this strain was investigated using gas chromatography-mass spectrometry. Twenty-one components were identified. 2-Phenylethanol (38.7%), E-ligustilide (12.4%), α-eudesmol (10.2%), β-vetivone (4.6%), β-ylangene (3.7%) and verbanol (3.4%) were the major components of the extract. The strong antibacterial activity of Ustilagosp. MFLUCC15-1024 ethyl acetate extract may be attributed to the presence of a high concentration of bioactive compounds including phenyl ethyl alcohol, E-ligustilide and α-eudesmol. The results indicate that there is high diversity of endophytic fungi in M. cordifolialeaf, and that Ustilagosp. MFLUCC15-1024 strain could be an excellent resource of natural antibacterial compounds.